1. Field of the Invention
The present invention relates to a playback apparatus, a playback method, a playback system and a recording medium for a program, and in particular relates to a playback apparatus, a playback method a playback system and a recording medium for a program that favorably remove silent sections between a plurality of decompressed digital data to allow the data to be played back without breaks in the sound.
2. Description of the Related Art
Content distribution systems are known in which, for example, sound/image contents are transmitted/received via a network between a client and a server provided with a communication function using TCP/IP. In such a content distribution system, the client requests transmission of a list of content and services that are provided by the server. Then, the content distribution system requests transmission of the content selected by a user based on the list received from the server, and in response to this request, the server transmits the contents, which are received and then played back by the content distribution system.
At this time, the client temporarily and sequentially stores the received content data in a buffer (buffering). When a determined volume of content data has been stored, the client starts playback. Note that, if the client is only capable of processing decompressed digital data such as, for example, linear PCM data or the like, the server decodes the compressed digital data that has been compression encoded using, for example, MP3 (MPEG-1 Layer 3) format encoding, converts the data into linear PCM data, and transmits it to the client.
However, in the known server described above, if music content, containing all of the tracks of a live performance album, for example, is transmitted to the client from the server, it is necessary for each piece of music content to be continuously played back at the client side. Normally, in a live performance, sound is still generated during the interval between tracks, and thus when a music compact disk (CD) of a recorded live performance is played back, the sound during the interval between tracks is also played back. However, in the known server, data that has been encoded using track units is generated, and distributed as music content. As a result, even if it is possible to transmit music content containing each track of an album from the server to the client, and for each track to be continuously played back at the client side, a silent period is generated between neighboring played back tracks. Thus, as compared to replaying a music CD, it is unavoidable that the music will sound unnatural. The reason for this will be explained in more detail next.
In compression encoding formats like MP3, a determined number of sample data is selected as one frame, and then compression encoding is performed using this frame unit. Note that, when compression data from the first track, some sample data are left that will not fit into one frame at the end section of the track. Given this, normally, sample data with a value of zero (hereinafter referred to as “zero data”) is added to form one frame, and then compression encoding is performed.
In the known server, compression encoding is performed using track units in this manner and then saved as music content. Accordingly, even if, hypothetically, encoded data for a plurality of track sections is continuously decoded and played back at the client side, the zero data is played back during the interval between tracks, thereby generating silent periods and breaks in the sound.
As one method of solving this problem, in the case of a live performance album, sample data for all the tracks on the album can be selected instead of track units, and then compression encoding can be performed on this group sample data. However, if this method is adopted, the server has to select all the tracks on the album and generate encoded data using compression encoding. As a result, when necessary data is transmitted to the client, it is not possible to replay just a specific track from the album or replay a specific track and the tracks following it.
In order to address the above-described problems, for example, Japanese Patent Application Publication No. JP-A-2006-30577 discloses a technology in which, when the server performs compression encoding on the music content, the start of the sample data of a second track is added to the end of the sample data of a first track to form one frame. Accordingly, the silent section between tracks is removed in advance at the server side, and then the music data is transmitted to the client.
Note that, Japanese Patent Application Publication No. JP-A-2004-318961 discloses a technology in which noise removal processing is performed on music content based on an analogue sound signal, and sections with a determined signal level or less are estimated to be the intervals between tracks. Then, the intervals between tracks are identified using information for identifying the intervals between tracks, whereby it is possible to accurately detect silent sections between the tracks included in the music content by suppressing the influence of noise.